Comparison of Snellen and ETDRS charts in visual acuity assessment: a systematic review Review article
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Abstract
The aim of this review is to compare the two most commonly used tools for assessing visual acuity: the Snellen chart and the ETDRS chart, in terms of their accuracy, reproducibility, and clinical utility in ophthalmic diagnostics. The Snellen chart, introduced in 1862, is widely used but its design can lead to interpretative errors, particularly when assessing patients with various eye conditions. The ETDRS chart, developed for diabetic retinopathy studies, offers greater precision due to its uniform progression in letter size and the use of the logMAR scale. A systematic review of the literature demonstrates that the ETDRS chart is characterised by higher accuracy, lower variability in results, and better reproducibility compared to the Snellen chart, especially in patient populations with cataracts, amblyopia, macular degeneration, and other retinal disorders. Although the ETDRS test takes longer to perform, its superior precision makes it the preferred choice for clinical studies, whereas the Snellen chart remains more practical for routine diagnostics. This review highlights the importance of selecting the appropriate tool for visual acuity assessment depending on the clinical context, suggesting that the ETDRS chart may be a better option in more demanding diagnostic cases.
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